Representative methods for analyzing the film quality and film thickness of a thin film include ellipsometry, which is a known old procedure. Ellipsometry is a procedure that inputs light in a specified polarization state to a thin-film sample and determines the film thickness and the refractive index of a sample and so forth by measuring the ratio ρ between the reflectance Rp of a component (p polarized wave) whose electric field is parallel to the incident face and the reflectance Rs of a component (s polarized wave) whose electric field is perpendicular to the incident face, in the light that is reflected by the sample. Here, ρ is generally a complex number and can be expressed as ρ=Rp/Rs=tan(ψ)×exp(jΔ). ψ and Δ are parameters that express the polarization state of the light (reflected light) to be measured and are known as ellipsometry angles. ρ is a value determined by the optical constant (n) and thickness (d) of the thin-film sample and, therefore, if the polarization state (ψ, Δ) of the reflected light can be determined by using an ellipsometer, the optical constant and film thickness of the sample can conversely be calculated.
As methods for determining ψ and Δ by performing polarization analysis of the reflected light from the sample by means of an ellipsometer, the quenching method and the rotating analyzer method and so forth that appear in documents in the Applied Physics Handbook (Applied Physics Society compilation, 1990, Maruzen, pages 20 to 22) have been used. The quenching method determines ψ and Δ by receiving the reflected light (generally elliptically polarized light) from the sample by means of an optical receiver after the light has passed through the ¼ wavelength plate and then the polarizer and then reading the rotation angle at which the optical intensity is minimum by independently rotating the ¼ wavelength plate and polarizer. However, because this method searches for the minimum value by means of two variables, there is the disadvantage that it takes a relatively long time even when performing only one measurement. One rotating analyzer method is a method that performs polarization analysis by using only the analyzer without using the ¼ wavelength plate. The rotating analyzer method measures the variation in the photoreception intensity when the polarizer is rotated once and, if the photoreception intensity is obtained as a function of the angle, ψ and Δ can be determined through calculation. However, there is the inconvenience that there is then no distinction of the phase difference from Δ (2π−Δ), that is, no distinction regarding whether this is a clockwise elliptically polarized light wave or a counterclockwise elliptically polarized light wave. Because it is necessary to perform measurement two or more times for the measurement of one point by inserting and removing the ¼ wavelength plate and so forth in order to avoid this problem, measurement is complicated and necessitates a great deal of time, which makes this method barely any different from the earlier quenching method.
Due to the marked progress of semiconductor technology in recent years, in the progress of various devices toward increased performance and miniaturization, the accuracy required of thin-film processes such as CVD and sputtering has become extremely strict and, for example, a film that is a few nanometers thick is also required to be made with an accuracy of 0.1 nm. Currently, in order to implement such highly accurate film deposition (or film-deposition devices), there is a great need for highly accurate film-thickness/film quality monitors that make it possible to perform inline measurement of the film thickness and film quality of the sample in the process. Ellipsometry is capable of accurately measuring the film thickness and film quality of thin films and is therefore said to be suited to such film-deposition monitor systems. However, conventional ellipsometry adopts complex measurement methods such as those mentioned earlier and, therefore, such devices are generally large-scale and highly expensive devices with a low measurement speed. Hence, the introduction of such devices into a process apparatus has proved difficult.
For a driverless polarization analysis device, a procedure for analyzing polarized wave states by measuring the optical intensity of four different polarized components by causing the light beam being measured to pass through respective polarizers or a wavelength plate and a polarizer after being divided into four has been proposed (Japanese Patent Application Laid Open No. H5-113371). Such a polarization measurement device is suited to simple and high-speed polarization analysis and the measurement principle has been well known for a long time as introduced in documents such as monocrystalline optics (Applied Physics Society Optics Conference, 1990, published by Morikita, pages 139 to 140). Therefore, in order to implement such a polarization analysis device, a large number of optical elements such as a beam splitter, polarizing beam splitter, ¼ wavelength plate, polarizer, and light-receiving element are required, and miniaturization of the device is difficult. Further, because it is very difficult to assemble the respective parts accurately, the measurement accuracy is poor and, therefore, an ellipsometer that necessitates highly accurate measurement of the thickness and optical constant of the thin film is not suitable.
As mentioned earlier, a procedure for analyzing the polarization state of incident light highly accurately by using a highly accurate and small-scale driverless polarization analysis device suited to ellipsometry has not yet been proposed.